By causing a laser beam emitted from a laser device to enter a wavelength conversion element, the laser beam of a desired wavelength can be provided, while the efficiency of a light source is reduced if such optical elements are joined together out of their proper relative position. Thus, the two optical elements are joined together after the relative position of the two optical elements has been adjusted to focus the light beam from the laser device on the wavelength conversion element.
There generally exist two methods of adjusting the relative position of two optical elements: one is called passive alignment, in which the relative position is adjusted with reference to the outer appearances of the optical elements or a target mark, or the relative position is mechanically determined by an abutment fit, and the other is called active alignment in which emission light from a laser device is caused to enter a wavelength conversion element, an amount of the outgoing laser light through the wavelength conversion element in operation is measured with a power meter or like means measures an amount of emitted light from the laser device with the wavelength conversion element in operation, and the position of the laser device or the wavelength conversion element is adjusted to move it three dimensionally so that the measured amount of the outgoing light becomes a maximum.
Of these, a suitable adjustment method is selectively used according to the circumstances, based on conditions such as functional accuracy in optical elements that configure a light source, a light output power to be required by the light source, and the like. An example of the active alignment includes a technique in which optical axes of the two optical elements are aligned so that the maximum amount of light is achieved by measuring an amount of the outgoing light that enters a first optical element from a second optical element and propagates within the second optical element to be caused to emit from the optical element (refer to Japanese Unexamined Patent Application Publication No. H01-180507, which hereinafter called Patent Document 1; and Japanese Unexamined Patent Application Publication No. 2004-109256, which is hereinafter called Patent Document 2).
Further, because the difference in temperatures between respective stages retaining the two optical elements causes different amount of variation in expansion/contraction of the stages, resulting in the retained optical elements being joined together with their misaligned positions, there is another example in which the two optical elements are joined together after the two stages have been heated and maintained at the same temperature (refer to Japanese Unexamined Patent Application Publication No. 2004-294594, which is hereinafter called Patent Document 3).
However, a problem is created in that when the temperatures of the optical elements are not controlled, as is the case with Patent Document 1 and Patent Document 2, or the stages retaining the two optical elements are heated at the same temperature, as is the case with Patent Document 3, high efficient light source cannot be provided because the optical elements is likely to significantly vary its characteristics by temperature and therefore its positions cannot properly be adjusted.